A broadcast message is useful to deliver the same message to multiple entities in a shorter time than delivering the message to each device independently. A broadcast message should be understood as intended to all entities able to understand the message. A multicast message is intended to subset of entities able to understand the message.
In a communication system, usually the reception of broadcast or multicast transmissions is not acknowledged. This avoids for example flooding of acknowledgements in the network after a broadcast transmission. Example of this are different wireless systems such as Wireless Local Area Network, WLAN, 802.11 where broadcast/multicast signals at Media Access Control, MAC, and Physical, PHY, layers are not acknowledged, also Layer 3, L3, Internet Protocol, IP, multicast packets are not acknowledged, and also Constrained Application Protocol, CoAP, group communication messages are not acknowledged. For this reason, broadcast/multicast transmissions are considered not reliable